Transport networks implement a key function of protection switching upon failure of network resources. Protections switching state machines are usually standardized for technologies that implement the capabilities as they require both end points to perform similar actions.
For example, IEEE802.1Qah [1] standardizes the separation of client services and transport servers. The related traffic engineering components were added in the IEEE802.1Qay standard. The IEEE802.1Qay standard initially specified a one for one (1:1) linear protection between a source and a destination in a network. This capability is accomplished using two tunnels or Traffic Engineered Service Instances (TESIs) which link the maintenance endpoints of the source and destination using a different path through the network. The two TESIs are combined at each end by a protection group which handles the decision of which of the TESIs is being used as the forwarding path at a given point based on their status. Each TESI is monitored by a Maintenance Association (MA) which monitors the status of the TESI using Continuity Check Messages (CCM). The status of the TESI is provided by the MA to the protection group, which in turn decides which TESI is being used as the forwarding path.
Referring to the network view in FIG. 1, a head endpoint system 108 and a tail endpoint system 109 are configured at the edge of the network. Services or clients use Backbone Service Instances (BSIs) 112, 113 as connections in each direction between the head and tail endpoint. The BSIs 112, 113 are switched on the working TESI 102, comprised of two Ethernet Switched Paths (ESPs) 115, 116. A protection TESI 104 is supplied using another set of ESPs 117, 118. Protection management is provided by the protection groups 110, 111. The MAs 101a, 101b and 103a, 103b provide the state of the TESIs 102, 104 to the protection groups 110, 111.
The MAs (one at the head and one at the tail) use Operation Administration and Maintenance (OAM) 105a, 105b, 106a, 106b, to check communication continuity in the TESI across the network 107 and establish the state of the TESIs 102, 104. The MAs 101a, 103a share the state with the associated protection group 110 which uses the state information to which the TESIs are set as active for the protection group 110. Similarly, the maintenance association 101b, 103b share their state with the associated protection group 111 which uses the state information to which TESI to set as active for the protection group 111. The services (or Backbone Service Instances) 112, 113 are mapped to the protection groups 110, 111 based on service provisioning policies. For simplicity, FIG. 1 represents unidirectional traffic flow, but the same TESI and OAM messages are used for the reverse direction of the traffic.
A non load-sharing architecture is used when a protection group is uniquely associated with one protection tunnel and one working TESI. FIG. 2 shows the non-load-sharing state machine at each end point of the TESI. Backbone Service Instances 201 are mapped to one of many protection groups 202 which is standardized in IEEE 802.1Qay. A working TESI 203 and a protection TESI 204 are associated with the protection group 202. A working MA 205 is associated with the working TESI 203. A protection maintenance association 206 is associated with the protection TESI 204. The maintenance associations 205, 206, receive the OAM flow from the working and protection TESIs 203, 204 and provide the protection group 202 with a state for its respective TESI. The protection group 202 uses the information provided by the MAs 205, 206 to select which TESIs 203, 204 are being used as the forwarding path to carry the traffic from the Backbone Service Instances 201.
There exist proposals to extend the 1:1 protection capability to allow sharing of TESI. However these proposals involve additional state machines with added complexity that directly affects scalability and implementability. There is a need to provide a simple extension to the 1:1 protection architecture to include the case where a protection TESI or a working TESI is shared by multiple protection groups to provide alternative protection schemes and minimize the use of protection resources. Ultimately, m protection groups could share n protection TESI where m<=n. There is also a need to use working TESIs as protection TESIs to enable load sharing and avoid bandwidth remaining idle while awaiting use for protection.